Author: Bruce Moreland
Date: 02:01:55 08/20/99
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On August 20, 1999 at 04:34:49, James Robertson wrote: >My program played a game in which this position arose: > >r3r1k1/3b1p1p/2p4q/p2p4/3P2p1/1PNPPpP1/P1RQ1P1P/5RK1 w - - > >It then played, after an 8 ply search, 1. e4?? which loses immediately to Qh3 >and the loss of the queen after 1. e4?? Qh3 2. Qg5+ 3. Qf8 Qh6+ 4. Qxh6, an >incredibly simple tactical sequence. I later ran my program on this position and >it switched to the much much better move Kh1 after 6 plies. > >The only differece I can think of between the two searches would be the hash >table? During the game it had entries from previous searches, and afterwards I >ran it as a testsuite position with a clean table. I cannot fathom why else my >program would miss such a thing in an actual game. Is there any reason why a >hash table would do this? Is there some depth/draft thing I am messing up with >my table? Is my null move causing problems? Any help anyone can provide is >greatly appreciated. > >James > >P.S. Here are the two searches: > >a) during the game. > >Depth Score Time Nodes PV > 1 216 0 35 Rfc1 > 2 200 0 250 e4 Qxd2 Rxd2 > 3 202 60 1263 Rfc1 Qh3 e4 > 4 203 170 9783 e4 Qg7 Qe3 Rab8 > 5 207 220 12885 e4 Qxd2 Rxd2 Be6 Rc1 > 6 202 330 20163 e4 Qxd2 Rxd2 Be6 Rc1 Rab8 Rdc2 > 7 199 550 40726 e4 Qxd2 Rxd2 Be6 Rc1 Rab8 Rdc2 Rb7 > 8 199 1050 89464 e4 Qxd2 Rxd2 Be6 Rc1 Rab8 Nb1 Rb6 Nc3 > >b) after the game with a fresh hash: > >Depth Score Time Nodes PV > 1 216 0 32 Rfc1 > 2 200 0 255 e4 Qxd2 Rxd2 > 3 202 270 1457 Rfc1 Qh3 e4 > 4 203 380 10068 e4 Qg7 Qe3 Rab8 > 5 199 440 14046 e4 Qxd2 Rxd2 Be6 Rc1 Rab8 > 6> -160 660 38006 Ne2 fxe2 Qxe2 a4 Rb1 Qh3 e4 axb3 Rxb3 > 6> -159 770 46432 b4 axb4 Nxd5 cxd5 Qxb4 Qh3 > 6> 50 770 47608 h4 gxh3 Kh2 > 6> 176 820 51711 Kh1 Qh3 Rg1 f5 Rcc1 Rab8 > 6 176 820 51949 Kh1 Qh3 Rg1 f5 Rcc1 Rab8 > 7 178 1100 76625 Kh1 Qh3 Rg1 f5 Rcc1 Rab8 Rge1 > 8 184 2250 191340 Kh1 Qh3 Rg1 f5 Qd1 Rab8 Qf1 Qxf1 Rxf1 > 9 184 5110 452120 Kh1 Qh3 Rg1 f5 Qd1 Rab8 Qf1 Qxf1 Rxf1 > 10 176 9060 845582 Kh1 Qh3 Rg1 f5 Rcc1 Rab8 Na4 Rb4 Nc5 Be6 I think you are flailing a bit. There can be any number of things going on differently in the real game case. You can have some problems involving transition from one position to the next, for instance you could be leaving things in a bogus state when you terminate a search. Also, when you start the program and immediately start a search, there are a lot of memory locations that are zeroed, which might not be zeroed the second time you start a search, and perhaps this is causing problems. A pure hash table problem, which would mean that you are totally off the hook and have to do nothing, is probably not what is causing this. This is an important bug for you to understand. bruce
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